Borrow my mobile phone?
I once found a little plastic 'walkie-talkie' on the ground. It wasn't a really one--just a simple toy that looked like one: a piece of soft grey plastic (well, two pieces, front and back). It was about the size of a mobile phone and in pretty bad shape. It was splitting along the seam, and the short antenna was falling apart (eventually it fell off entirely). No photo, sadly.
So what did I do with this useless piece of trash? I put it in my pocket and carried it around with me for about a year. During that year, I only had one opportunity to lend someone my 'mobile phone', though it came out once at the Philosophy Club too for some reason. Two years in my pocket for one or two jokes.
Well worth it.